Golf ball

ABSTRACT

An object of the present invention is to provide a golf ball showing increased controllability on approach shots for less than 40 yards and showing excellent shot feeling. In the inventive golf ball, the paint film is formed from a curing type paint composition including: a base material containing a polyrotaxane, and a curing agent containing a polyisocyanate, and wherein the polyrotaxane has a cyclodextrin, a linear molecule included in a cyclic structure of the cyclodextrin in a manner of piercing through the cyclic structure of the cyclodextrin, and a blocking group located at both ends of the linear molecule to prevent disassociation of the cyclodextrin, and at least a part of hydroxyl groups of the cyclodextrin is modified with a caprolactone chain via —O—C3H6—O— group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of pending U.S. patent applicationSer. No. 14/941,315, filed on Nov. 13, 2015, now U.S. Pat. No. 9,656,126which claims priority to Japanese Patent Application No. 2014-232205,filed on Nov. 14, 2014. The entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a technology for improving spinperformance of a golf ball.

DESCRIPTION OF THE RELATED ART

A paint film is formed on a surface of a golf ball body. Improvement ofa golf ball performance by improving the paint film has been proposed.

Japanese Patent Publication No. 2011-67595 A discloses a golf ballcomprising a core, a cover situated on the external side of the core,and a paint layer situated on the external side of the cover, whereinthe cover has a Shore D hardness of 61 or less, and the paint layer hasa Martens hardness of 2.0 mgf/μm² or less. The golf ball is excellent inspin performance, spin rate stability and paint layer durability.

Japanese Patent Publication No. 2011-217820 A discloses a golf ballcomprising a golf ball body and a paint film formed on a surface of thegolf ball body, wherein the paint film has a Martens hardness of 2.0mgf/μm² or less, and a ratio (50% elastic modulus/10% elastic modulus)of a 50% elastic modulus to a 10% elastic modulus of 1.6 or more. Thegolf ball has a high spin rate on approach shots under a wet conditionand rough condition.

Japanese Patent Publications No. 2006-75209 A and No. 2006-75210 A haveproposed a golf ball stopping quickly with an increased launch angle.Japanese Patent Publication No. 2006-75209 A discloses a golf ballcomprising a golf ball body and a paint film covering a surface of thegolf ball body, wherein a resin component constituting the paint film iscured by a polyamide based curing agent, and the golf ball has a staticcoefficient of friction of 0.22 or less. Japanese Patent Publication No.2006-75210 A discloses a golf ball comprising a golf ball body and apaint film covering the golf ball body, wherein the paint film containsmetal particles.

Japanese Patent Publication No. 2000-288125 A has proposed a golf ballshowing improved durability and abrasion resistance. The golf ballshowing excellent durability comprises a core, a cover and at least onepaint layer formed on the cover, wherein the cover has a Shore Dhardness ranging from 50 to 65 and a bending flexural modulus rangingfrom 1,000 to 2,000 kgf/cm², and at least an outermost layer of thepaint has a 10% modulus of from 5 to 50 kgf/cm².

Japanese Patent Publication No. 2003-265650 A has proposed a golf ballshowing improved spin retention ratio without sacrificing the requiredproperties for the paint film. The golf ball comprises a core, at leastone cover layer covering the core and a paint film formed on an outersurface of the cover, wherein the paint film has a thickness fallingwithin a range of 25 μm or more and 125 μm or less and a 50% modulusfalling within a range of 5 MPa or more and 50 MPa or less, and Rexpressed by a following equation (1) falls within a range of 0.01 ormore and 0.5 or less, when CL (mm) represents a thickness of anoutermost layer of the cover, and PL (μm) represents the thickness ofthe paint film;R=PL/CL/1,000  (1).

SUMMARY OF THE INVENTION

It is needless to say that not only flight distance on driver shots butalso accuracy on approach shots are important in making a score in golf.A golf ball employing a relatively flexible thermoplastic polyurethaneas a cover material is excellent in controllability on approach shotsfor a distance of about 40 yards to 100 yards. However, almost noconsideration is given to controllability on approach shots for lessthan 40 yards, in particular, for about 10 yards to 20 yards, i.e.around the green. In addition, no consideration is given tocontrollability on approach shots from the rough.

The present invention has been made in view of the above-describedsituation, and an object of the present invention is to provide a golfball showing improved controllability on approach shots for less than 40yards, in particular, on approach shots around the green (about 10 yardsto 20 yards) and improved controllability on approach shots from therough, and showing excellent shot feeling.

The golf ball according to the present invention comprises a golf ballbody and a paint film formed on a surface of the golf ball body, whereinthe paint film is formed from a curing type paint composition including:a base material containing a polyrotaxane, and a curing agent containinga polyisocyanate, and wherein the polyrotaxane has a cyclodextrin, alinear molecule included in a cyclic structure of the cyclodextrin in amanner of piercing through the cyclic structure of the cyclodextrin, andhaving blocking groups located at both ends of the linear molecule toprevent disassociation of the cyclodextrin, and at least a part ofhydroxyl groups of the cyclodextrin is modified with a caprolactonechain via —O—C₃H₆—O— group. The hydroxyl group of the cyclodextrinincluded in the polyrotaxane reacts with the isocyanate group of thepolyisocyanate to form the paint film. The golf ball having this paintfilm formed on the surface of the golf ball body is excellent incontrollability on approach shots for less than 40 yards, in particular,on approach shots around the green (about 10 yards to 20 yards), and isexcellent in shot feeling.

According to the present invention, a golf ball showing improvedcontrollability on approach shots for less than 40 yards, in particular,on approach shots around the green (about 10 yards to 20 yards) andimproved controllability on approach shots from the rough, and showingexcellent shot feeling, can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway cross-sectional view of a golf ballaccording to an embodiment of the present invention;

FIG. 2 is a schematic view of an example of a contact force tester usedin the present invention;

FIG. 3 is a partially enlarged cross-sectional view of a collision plateof the contact force tester;

FIG. 4 is a graph illustrating an example of Ft(t), Fn(t) and M(t);

FIG. 5 is a cross-sectional view of a groove shape of a surface layermaterial of the contact force tester;

FIG. 6 is a graph illustrating an example of Ft(t), Fn(t) and M(t);

FIG. 7 is an explanatory drawing illustrating an embodiment of formingslits on a wet paper when measuring a coefficient of friction (wet); and

FIG. 8 is a schematic view showing an embodiment of painting with an airgun.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The golf ball according to the present invention comprises a golf ballbody and a paint film formed on a surface of the golf ball body, whereinthe paint film is formed from a curing type paint composition including:a base material containing a polyrotaxane, and a curing agent containinga polyisocyanate, and wherein the polyrotaxane has a cyclodextrin, alinear molecule included in a cyclic structure of the cyclodextrin in amanner of piercing through the cyclic structure of the cyclodextrin, andhaving blocking groups located at both ends of the linear molecule toprevent disassociation of the cyclodextrin, and at least a part ofhydroxyl groups of the cyclodextrin is modified with a caprolactonechain via —O—C₃H₆—O— group.

[Polyrotaxane]

First, the base material will be described. The base material contains apolyrotaxane as a resin component. The polyrotaxane has a cyclodextrin,a linear molecule piercing through the cyclic structure of thecyclodextrin, and having blocking groups located at both ends of thelinear molecule to prevent disassociation of the ring molecule. Thepolyrotaxane is viscoelastic, since the cyclodextrin molecule is movablealong the linear molecule that penetrates the cyclodextrin in askewerring manner (pulley effect). Even if a tension is applied to thepolyrotaxane, the tension can be uniformly dispersed due to the pulleyeffect. Thus, the polyrotaxane has an excellent property that a crack orflaw very hardly occurs, unlike a conventional crosslinked polymer.

The cyclodextrin is a general term for an oligosaccharide having acyclic structure. The cyclodextrin is, for example, a molecule having 6to 8 D-glucopyranose residues being linked in a cyclic shape via anα-1,4-glucoside bond. Examples of the cyclodextrin includeα-cyclodextrin (number of glucose units: 6), β-cyclodextrin (number ofglucose units: 7), and γ-cyclodextrin (number of glucose units: 8), andα-cyclodextrin is preferable. As the cyclodextrin, one type may be usedsolely, and two or more types may be used in combination.

The linear molecule is not particularly limited, as long as it is alinear molecule capable of piercing through the cyclic structure of thecyclodextrin so that the cyclic structure of the cyclodextrin isrotatable around the linear molecule. Examples of the linear moleculeinclude polyalkylene, polyester, polyether, and polyacrylic acid. Amongthem, polyether is preferable, and polyethylene glycol is particularlypreferable. Polyethylene glycol has less steric hindrance, and thus canbe easily included in the cyclic structure of the cyclodextrin in amanner of piercing through the cyclic structure of the cyclodextrin.

The weight average molecular weight of the linear molecule is preferably5,000 or more, more preferably 6,000 or more, and is preferably 100,000or less, more preferably 80,000 or less.

The linear molecule preferably has functional groups at both endsthereof. When the linear molecule has the functional group, the linearmolecule can easily react with the blocking group. Examples of thefunctional group include a hydroxyl group, carboxyl group, amino group,and thiol group.

The blocking groups are not particularly limited, as long as they arelocated at both ends of the linear molecule to prevent the cyclodextrinfrom disassociating from the linear molecule. Examples of the method forpreventing the disassociation include a method of using a bulky blockinggroup to physically prevent the disassociation, and a method of using anionic blocking group to electrostatically prevent the disassociation.Examples of the bulky blocking group include a cyclodextrin and anadamantyl group. The number (inclusion amount) of the cyclodextrinsincluding the linear molecule preferably ranges from 0.06 to 0.61, morepreferably ranges from 0.11 to 0.48, even more preferably ranges from0.24 to 0.41, if the maximum inclusion amount is deemed as 1. This isbecause if the inclusion amount is less than 0.06, the pulley effect maynot be exerted, and if the inclusion amount exceeds 0.61, thecyclodextrins are very densely located, so that the movability of thecyclodextrin may decrease.

As the polyrotaxane used in the present invention, a polyrotaxan havingat least a part of hydroxyl groups of the cyclodextrin being modifiedwith a caprolactone chain, is preferred. This is because if at least apart of hydroxyl groups of the cyclodextrin included in the polyrotaxaneis modified with the caprolactone, steric hindrance between thepolyrotaxane and the polyisocyanate is alleviated, so that theefficiency of a reaction with the polyisocyanate increases.

As the above modification, for example, the hydroxyl groups of thecyclodextrin are treated with propylene oxide to hydroxylalkylate thecyclodextrin, and then ε-caprolactone is added to perform ring-openingpolymerization. As a result of this modification, the caprolactone chain—(CO(CH₂)₅O)nH (n is a natural number of 1 to 100) is linked to theexterior side of the cyclic structure of the cyclodextrin via —O—C₃H₆—O—group. “n” represents the degree of polymerization, and is preferably anatural number of 1 to 100, more preferably a natural number of 2 to 70,even more further preferably a natural number of 3 to 40. At the otherend of the caprolactone chain, a hydroxyl group is formed through thering-opening polymerization. The hydroxyl group at the end of thecaprolactone chain can react with the polyisocyanate.

The ratio of the hydroxyl groups modified with the caprolactone chain toall the hydroxyl groups (100 mole %) included in the cyclodextrin beforethe modification is preferably 2 mole % or more, more preferably 5 mole% or more, even more preferably 10 mole % or more. If the ratio of thehydroxyl groups modified with the caprolactone chain falls within theabove range, the hydrophobicity of the polyrotaxane increases, and thereactivity with the polyisocyanate increases.

The hydroxyl value of the polyrotaxane is preferably 10 mg KOH/g ormore, more preferably 15 mg KOH/g or more, even more preferably 20 mgKOH/g or more, and is preferably 400 mg KOH/g or less, more preferably300 mg KOH/g or less, even more preferably 220 mg KOH/g or less,particularly preferably 180 mg KOH/g or less. If the hydroxyl value ofthe polyrotaxane falls within the above range, the reactivity with thepolyisocyanate increases, and thus the durability of the paint filmbecomes more favorable. The hydroxyl value can be measured according toJIS K 1557-1, for example, by an acetylation method.

The total molecular weight of the polyrotaxane is preferably 30,000 ormore, more preferably 40,000 or more, even more preferably 50,000 ormore, and is preferably 3,000,000 or less, more preferably 2,500,000 orless, even more preferably 2,000,000 or less, in a weight averagemolecular weight. If the weight average molecular weight is 30,000 ormore, the paint film has sufficient strength, and if the weight averagemolecular weight is 3,000,000 or less, the paint film has sufficientflexibility and thus approach performance of the golf ball increases. Itis noted that the weight average molecular weight of the polyrotaxanecan be measured, for example, by gel permeation chromatography (GPC)using polystyrene as a standard substance, tetrahydrofuran as an eluant,and an organic solvent GPC column (e.g., “Shodex (registered trademark)KF series” manufactured by Showa Denko K.K.) as a column.

The content of the polyrotaxane in the resin component of the basematerial is preferably 10 mass % or more, more preferably 15 mass % ormore, even more preferably 20 mass % or more, and is preferably 100 mass% or less, more preferably 90 mass % or less, even more preferably 85mass % or less.

Specific examples of the polyrotaxane modified with the polycaprolactoneinclude SeRM super polymer SH3400P, SH2400P, and SH1310P manufactured byAdvanced Softmaterials Inc.

[Other Polyol]

In the present invention, the base material preferably further contains,as a resin component, at least one polyol selected from the groupconsisting of a polyether polyol, a polyester polyol, a polycaprolactonepolyol, a polycarbonate polyol, and an acrylic polyol.

Examples of the polyol include a polyether polyol such aspolyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), andpolyoxytetramethylene glycol (PTMG); a polyester polyol such aspolyethylene adipate (PEA), polybutylene adipate (PBA), andpolyhexamethylene adipate (PHMA); a polycaprolactone polyol such aspoly-ε-caprolactone (PCL); a polycarbonate polyol such aspolyhexamethylene carbonate; and an acrylic polyol. The polyol ispreferably a diol or triol, and is more preferably a triol. The polyolmay be used solely, or two or more of the polyols may be used incombination.

In the present invention, the curing type paint composition preferablyincludes the polycaprolactone polyol (poly-ε-caprolactone (PCL)) as thepolyol. Specific examples of the polycaprolactone polyol include Placcel308 and Placcel 312 manufactured by Daicel Chemical Industries, Ltd.,and Capa 4101 and Capa 4801 (having a typical molecular weight of 8,000)manufactured by Perstorp Co., Ltd.

The hydroxyl value of the polyol is preferably 10 mg KOH/g or more, morepreferably 15 mg KOH/g or more, even more preferably 20 mg KOH/g ormore, and is preferably 400 mg KOH/g or less, more preferably 300 mgKOH/g or less, even more preferably 250 mg KOH/g or less, particularlypreferably 200 mg KOH/g or less. If the hydroxyl value of the polyolfalls within the above range, the adhesion between the paint film andthe golf ball body increases. In the present invention, the hydroxylvalue can be measured according to JIS K 1557-1, for example, by anacetylation method.

The weight average molecular weight of the polyol is preferably 500 ormore, more preferably 550 or more, even more preferably 600 or more, andis preferably 150,000 or less, more preferably 140,000 or less, evenmore preferably 130,000 or less. If the weight average molecular weightof the polyol falls within the above range, water resistance and impactresistance of the paint film can be increased. It is noted that theweight average molecular weight of the polyol can be measured, forexample, by gel permeation chromatography (GPC) using polystyrene as astandard substance, tetrahydrofuran as an eluant, and an organic solventGPC column (e.g., “Shodex (registered trademark) KF series” manufacturedby Showa Denko K.K.) as a column.

The content of the polyol in the resin component contained in the basematerial is preferably 0 mass % or more, more preferably 5 mass % ormore, even more preferably 10 mass % or more, and is preferably 90 mass% or less, more preferably 85 mass % or less, even more preferably 80mass % or less. The mass ratio (polyol/polyrotaxane) of the polyol tothe polyrotaxane is preferably 0/100 or more, more preferably 5/95 ormore, even more preferably 10/90 or more, and is preferably 90/10 orless, more preferably 85/15 or less, even more preferably 80/20 or less.

The curing type paint composition used in the present invention mayfurther include, as a resin component, a vinyl chloride-vinyl acetatecopolymer and/or a modified product thereof. This is because, if thevinyl chloride-vinyl acetate copolymer and/or the modified productthereof is included, the adhesion can be adjusted while maintainingscuff resistance, and moderate tacky feeling is obtained. Examples ofthe modification method include a method of copolymerizing a monomer(e.g., vinyl alcohol, hydroxyalkyl acrylate, etc.) copolymerizable withvinyl chloride and vinyl acetate; and a method of partially orcompletely saponifying a vinyl chloride-vinyl acetate copolymer tointroduce hydroxyl groups therein.

The content of the vinyl chloride component in the vinyl chloride-vinylacetate copolymer and/or the modified product thereof is preferably 1mass % or more, more preferably 20 mass % or more, even more preferably50 mass % or more, and is preferably 99 mass % or less, more preferably95 mass % or less. In the present invention, as the vinyl chloride-vinylacetate copolymer and/or the modified product thereof, a hydroxylgroup-modified vinyl chloride-vinyl acetate copolymer is preferablyused. Specific examples of the vinyl chloride-vinyl acetate copolymerand/or the modified product thereof include Solbin (registeredtrademark) A, Solbin AL, Solbin TA2, and Solbin TA3 manufactured byNissin Chemical Industry Co., Ltd.

The curing type paint composition used in the present inventionpreferably further includes a modified silicone. If the modifiedsilicone is included as a leveling agent, unevenness of the coatedsurface can be reduced, and thus a smooth coated surface can be formedon the surface of the golf ball. Examples of the modified siliconeinclude a modified silicone having an organic group being introduced toa side chain or an end of a polysiloxane skeleton, a polysiloxane blockcopolymer obtained by copolymerizing a polyether block and/or apolycaprolactone block, etc. with a polysiloxane block, and a modifiedsilicone having an organic group being introduced to a side chain or anend of the polysiloxane block copolymer. The polysiloxane skeleton orthe polysiloxane block is preferably linear, and examples thereofinclude dimethyl polysiloxane, methylphenyl polysiloxane, and methylhydrogen polysiloxane. Examples of the organic group include an aminogroup, epoxy group, mercapto group, and carbinol group. In the presentinvention, as the modified silicone oil, apolydimethylsiloxane-polycaprolactone block copolymer is preferablyused, and a terminal carbinol-modifiedpolydimethylsiloxane-polycaprolactone block copolymer is more preferablyused. This is because these block copolymers have excellentcompatibility with the caprolactone-modified polyrotaxane and thepolycaprolactone polyol. Specific examples of the modified silicone usedin the present invention include DBL-C31, DBE-224, and DCE-7521manufactured by Gelest, Inc.

Next, the curing agent will be described. The curing agent contains apolyisocyanate. Examples of the polyisocyanate include a compound havingat least two isocyanate groups.

Examples of the polyisocyanate include an aromatic polyisocyanate suchas 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI),4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate(NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate(XDI), tetramethylxylylene diisocyanate (TMXDI), para-phenylenediisocyanate (PPDI); an alicyclic polyisocyanate or aliphaticpolyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI),hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate(HDI), isophorone diisocyanate (IPDI), and norbornene diisocyanate(NBDI); and derivates of these polyisocyanates. In the presentinvention, as the polyisocyanate, two or more of them may be used.

Examples of the derivative of the polyisocyanate include an isocyanurateof diisocyanate; an adduct obtained through a reaction between adiisocyanate and a low molecular weight triol such as trimethylolpropaneor glycerin; an allophanate-modified product; and a biuret-modifiedproduct. It is preferable that a free diisocyanate is removed from thederivative of the polyisocyanate. The allophanate-modified product is,for example, a trifunctional polyisocyanate obtained by further reactinga diisocyanate with a urethane bond formed through a reaction between adiisocyanate and a low molecular weight diol. The biuret-modifiedproducts is, for example, a trifunctional polyisocyanate having a biuretbond and represented by the following formula (1). The isocyanurate ofdiisocyanate is, for example, a trifunctional polyisocyanate representedby the following formula (2).

It is noted that in the formulae (1) and (2), R represents a residuewhere the isocyanate group is removed from the diisocyanate.

In the present invention, as the polyisocyanate, the isocyanurate ispreferably used, and the isocyanurate of hexamethylene diisocyanate ismore preferably used.

The content (NCO %) of the isocyanate group in the polyisocyanate ispreferably 0.5 mass % or more, more preferably 1 mass % or more, evenmore preferably 2 mass % or more, and is preferably 45 mass % or less,more preferably 40 mass % or less, even more preferably 35 mass % orless. It is noted that the content (NCO %) of the isocyanate group inthe polyisocyanate can be represented by 100×[mole number of isocyanategroup in polyisocyanate×42 (molecular weight of NCO)]/[total mass (g) ofpolyisocyanate].

Specific examples of the polyisocyanate include Burnock D-800, BurnockDN-950, and Burnock DN-955 manufactured by DIC corporation; DesmodurN75MPA/X, Desmodur N3300, Desmodur N3390, Desmodur L75 (C), and SumidurE21-1 manufactured by Sumika Bayer Urethane Co., Ltd; Coronate HX, andCoronate HK manufactured by Nippon Polyurethane Industry Co., Ltd;Duranate 24A-100, Duranate 21S-75E, Duranate TPA-100, and DuranateTKA-100 manufactured by Asahi Kasei Chemicals Corporation; and VESTANATT1890 manufactured by Degussa Co., Ltd.

The curing type paint composition used in the present invention includesa base material containing the polyrotaxane and a curing agentcontaining the polyisocyanate. In the present invention, in order todistinguish the composition containing the polyrotaxane and thecomposition containing the polyisocyanate, as a matter of convenience,the composition containing the polyrotaxane is referred to as the basematerial, and the composition containing the polyisocyanate is referredto as the curing agent. In addition, the base material may also bereferred to as the A agent, and the curing agent may also be referred toas the B agent. Furthermore, the composition containing the polyrotaxanemay also be referred to as the curing agent, and the compositioncontaining the polyisocyanate may also be referred to as the basematerial.

In the curing type paint composition used in the present invention, thebase material preferably contains a compound having reactivity with theisocyanate group included in the curing agent. Specifically, the basematerial contains the polyrotaxane, and preferably further contains apolyol. The base material of the curing type paint compositionpreferably contains a vinyl chloride-vinyl acetate copolymer and/or amodified product thereof, and a modified silicone.

In this case, the content of the vinyl chloride-vinyl acetate copolymerand/or the modified product thereof in the resin component of the basematerial is preferably 4 mass % or more, more preferably 8 mass % ormore, and is preferably 50 mass % or less, more preferably 45 mass % orless. The content of the modified silicone is preferably 0.01 part bymass or more, more preferably 0.05 part by mass or more, and ispreferably 10 parts by mass or less, more preferably 5 parts by mass orless, with respect to 100 parts by mass of the resin component in thebase material.

In the curing reaction of the curing type paint composition, the molarratio (NCO group/OH group) of the isocyanate group (NCO group) of thecuring agent to the hydroxyl group (OH group) of the base material ispreferably 0.1 or more, more preferably 0.2 or more. If the molar ratio(NCO group/OH group) is less than 0.1, the curing reaction may becomeinsufficient. Further, if the molar ratio (NCO group/OH group) is toolarge, the amount of the isocyanate group is excessive, and the obtainedpaint film may become hard and fragile as well as the appearance of theobtained paint film may deteriorate. Thus, the molar ratio (NOC group/OHgroup) is preferably 1.5 or less, more preferably 1.4 or less, even morepreferably 1.3 or less. The reason why the appearance of the obtainedpaint film deteriorates if the amount of the isocyanate group in thepaint becomes excessive is that an excessive amount of the isocyanategroup may promote a reaction between the moisture in the air and theisocyanate group, thereby generating a lot of carbon dioxide gas. It isnoted that, when the NCO/OH molar ratio in the curing reaction is takeninto account, the hydroxyl group of the base material includes thehydroxyl groups of the polyrotaxane and the polyol, but excludes thehydroxyl groups of the modified product of the vinyl chloride-vinylacetate copolymer, the modified silicone, and the like.

[Solvent]

The curing type paint composition is preferably a solvent based paintcontaining an organic solvent as a dispersion medium. This is becausethe polyrotaxane is insoluble in water, and the organic solvent ispreferably used. Examples of the preferable solvent include toluene,isopropyl alcohol, xylene, methylethyl ketone, methylisobutyl ketone,ethylene glycol monomethyl ether, ethylbenzene, propylene glycolmonomethyl ether, isobutyl alcohol, and ethyl acetate. The solvent maybe added in either of the base material and the curing agent, and inlight of uniformly performing the curing reaction, the solvent ispreferably added in the base material and the curing agent,respectively.

A conventionally known catalyst can be employed for the curing reaction.Examples of the catalyst include a monoamine such as triethyl amine andN,N-dimethylcyclohexylamine; a polyamine such asN,N,N′,N′-tetramethylethylene diamine andN,N,N′,N″,N″-pentamethyldiethylene triamine; a cyclic diamine such as1,8-diazabicyclo[5.4.0]-7-undecene (DBU) and triethylene diamine; a tincatalyst such as dibutyl tin dilaurate and dibutyl tin diacetate. Thesecatalysts may be used solely, or two or more of the catalysts may beused in combination. Among them, the tin catalyst such as dibutyl tindilaurate and dibutyl tin diacetate is preferred, and in particular,dibutyl tin dilaurate is preferably used.

The curing type paint composition may further include additivesgenerally included in the paint for a golf ball, such as a filler,ultraviolet absorber, antioxidant, light stabilizer, fluorescentbrightener, anti-blocking agent, leveling agent, slip agent, andviscosity modifier, where necessary.

Next, the method of applying the curing type paint composition of thepresent invention will be described. The method of applying the curingtype paint composition is not limited, a conventionally known method canbe adopted, and examples thereof include a spray coating andelectrostatic coating.

In the case of performing the spray coating with an air gun, the basematerial and the curing agent are fed with respective pumps andcontinuously mixed with a line mixer located in the stream line justbefore the air gun, and the obtained mixture is air-sprayed.Alternatively, the base material and the curing agent are air-sprayedrespectively with an air spray system provided with a device forcontrolling the mixing ratio thereof. The paint application may beconducted by spraying the paint one time or overspraying the paintmultiple times.

The curing type paint applied to the golf ball body can be dried, forexample, at a temperature ranging from 30° C. to 70° C. for 1 hour to 24hours to form the paint film.

The thickness of the paint film after drying is preferably, withoutlimitation, 5 μm or more, more preferably 6 μm or more, even morepreferably 10 μm or more, most preferably 15 μm or more. If thethickness is less than 5 μm, the paint film is likely to wear off due tothe continued use, and thickening the paint film increases the spin rateon approach shots. The thickness of the paint film is preferably 50 μmor less, more preferably 45 μm or less, even more preferably 40 μm orless. If the thickness of the paint film is thicker than 50 μm, thedimple effect is lowered, and thus the flying performance of the golfball tends to be lowered. The thickness of the paint film can bemeasured, for example, by observing a cross section of the golf ballusing a microscope (VHX-1000 manufactured by Keyence Corporation). Inthe case of overpainting the paint, a total thickness of the formedpaint film preferably falls within the above range.

The 10% elastic modulus of the paint film formed on the surface of thegolf ball body according to the present invention is preferably 160kgf/cm² or less, more preferably 130 kgf/cm² or less, even morepreferably 110 kgf/cm² or less. If the 10% elastic modulus is 160kgf/cm² or less, the paint film is flexible and the spin rate onapproach shots increases. The lower limit of the 10% elastic modulus ofthe paint film is not particularly limited, and is preferably 4 kgf/cm²,more preferably 6 kgf/cm². If the 10% elastic modulus is excessivelylow, the paint film becomes so soft that tackiness is left and feelingbecomes worse.

[Golf Ball Body]

The golf ball according to the present invention is not particularlylimited, as long as it is a golf ball comprising a golf ball body and apaint film formed on a surface of the golf ball body. The constructionof the golf ball body is not particularly limited, and the golf ballbody may be a one-piece golf ball, a two-piece golf ball, a three-piecegolf ball, a four-piece golf ball, a multi-piece golf ball such as afive-piece golf ball and a golf ball comprising more than five pieces,or a wound golf ball. The present invention can be applied appropriatelyto any one of the above golf balls.

FIG. 1 is a partially cutaway view showing a golf ball 2 according to anembodiment of the present invention. The golf ball 2 comprises aspherical core 104, an intermediate layer 106 covering the sphericalcore 104, a cover 112 covering the intermediate layer 106. On thesurface of the cover 112, a plurality of dimples 114 are formed. On thesurface of the golf ball, a part other than the dimples 114 is a land116. The golf ball further comprises a paint layer and a mark layer onthe outer side of the cover, but these layers are not depicted.

The golf ball according to the present invention is preferably a golfball comprising a core and a cover covering the core. In this case, thecover preferably has a hardness of 70 or less, more preferably 65 orless, even more preferably 60 or less, most preferably 50 or less inShore D hardness. If the cover has a hardness of 70 or less in Shore Dhardness, the spin rate on approach shots for a distance of about 40yards to about 100 yards becomes higher, and thus controllabilityincreases. The lower limit of the hardness of the cover is notparticular limited, but it is preferably 10, more preferably 15, evenmore preferably 20 in Shore D hardness. The hardness of the cover is aslab hardness obtained by measuring a cover composition for forming thecover molded into a sheet form.

The cover material constituting the cover of the golf ball according tothe present invention is not particularly limited, and examples thereofinclude various resins such as an ionomer resin, a polyester resin, aurethane resin like a thermoplastic urethane resin or a two-componentcuring type urethane resin, and a polyamide resin; and a thermoplasticpolyamide elastomer having a trade name of “Pebax (registered trademark)(e.g. “Pebax 2533”)” commercially available from Arkema Inc., athermoplastic polyester elastomer having a trade name of “Hytrel(registered trademark) (e.g. “Hytrel 3548” and “Hytrel 4047”)”commercially available from Du Pont-Toray Co., Ltd., a thermoplasticpolyurethane elastomer having a trade name of “Elastollan (registeredtrademark) (e.g. “Elastollan XNY97A”)” available from BASF Japan Ltd,and a thermoplastic styrene elastomer having a trade name of “Rabalon(registered trademark)” and a thermoplastic polyester elastomer having atrade name of “Primalloy” commercially available from MitsubishiChemical Corporation. These cover materials may be used solely, or twoor more of these cover materials may be used in combination.

The cover may include a pigment component such as a white pigment (e.g.titanium oxide), a blue pigment and a red pigment, a weight adjustingagent such as calcium carbonate and barium sulfate, a dispersant, anantioxidant, an ultraviolet absorber, a light stabilizer, a fluorescentmaterial or a fluorescent brightener, or the like, in addition to theabove resin component, as long as they do not impair the performance ofthe cover.

The embodiment for molding the cover from the cover composition is notparticularly limited, and examples thereof include an embodimentcomprising injection molding the cover composition directly onto thecore; and an embodiment comprising molding the cover composition intohollow shells, covering the core with a plurality of the hollow shellsand compression molding the core with a plurality of the hollow shells(preferably an embodiment comprising molding the cover composition intohalf hollow-shells, covering the core with two of the half hollow-shellsand compression molding the core with two of the half hollow-shells).After the cover is molded, the obtained golf ball body is ejected fromthe mold, and as necessary, the golf ball body is preferably subjectedto surface treatments such as deburring, cleaning, and sandblast. Ifdesired, a mark may be formed.

The total number of the dimples formed on the cover is preferably 200 ormore and 500 or less. If the total number of the dimples is less than200, the dimple effect is hardly obtained. If the total number exceeds500, the dimple effect is hardly obtained because the size of therespective dimples is small. The shape (shape in a plan view) of theformed dimple includes, for example, without limitation, a circle; apolygonal shape such as a roughly triangular shape, a roughlyquadrangular shape, a roughly pentagonal shape, and a roughly hexagonalshape; and another irregular shape. The shape may be employed solely, ortwo or more of the shapes may be employed in combination.

The golf ball preferably has a diameter ranging from 40 mm to 45 mm. Inlight of satisfying a regulation of US Golf Association (USGA), thediameter is preferably 42.67 mm or more. In light of prevention of theair resistance, the diameter is preferably 44 mm or less, morepreferably 42.80 mm or less. The golf ball preferably has a mass of 40 gor more and 50 g or less. In light of obtaining greater inertia, thegolf ball more preferably has a mass of 44 g or more, even morepreferably 45.00 g or more. In light of satisfying a regulation of USGA,the golf ball preferably has a mass of 45.93 g or less.

When the golf ball according to the present invention has a diameterranging from 40 mm to 45 mm, the compression deformation amount(shrinking amount along the compression direction) of the golf ball whenapplying a load from 98 N as an initial load to 1275 N as a final loadto the golf ball is preferably 2.0 mm or more, more preferably 2.2 mm ormore, and is preferably 4.0 mm or less, more preferably 3.5 mm or less.If the compression deformation amount is 2.0 mm or more, the golf balldoes not become excessively hard and thus the shot feeling thereofbecomes better. On the other hand, if the compression deformation amountis 4.0 mm or less, the resilience of the golf ball becomes better.

Next, the core used for a wound golf ball, two-piece golf ball andmulti-piece golf ball, and the one-piece golf ball body will beexplained.

The core or the one-piece golf ball body may use a conventionally knownrubber composition (hereinafter simply referred to as “core rubbercomposition” occasionally), and may be formed by heat pressing, forexample, a rubber composition containing a base rubber, aco-crosslinking agent and a crosslinking initiator.

As the base rubber, particularly preferred is a high cis-polybutadienehaving a cis-bond in a proportion of 40 mass % or more, more preferably70 mass % or more, and even more preferably 90 mass % or more in view ofits advantageous resilience. As the co-crosslinking agent, anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metalsalt thereof is preferable, and a metal salt of acrylic acid or a metalof methacrylic acid is more preferable. As the metal constituting themetal salt, zinc, magnesium, calcium, aluminum or sodium is preferable,and zinc is more preferable. The amount of the co-crosslinking agent tobe used is preferably 20 parts by mass or more and 50 parts by mass orless, with respect to 100 parts by mass of the base rubber. As thecrosslinking initiator, an organic peroxide is preferably used. Specificexamples of the organic peroxide include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferably used. The amount of thecrosslinking initiator to be used is preferably 0.2 part by mass ormore, more preferably 0.3 part by mass or more, and is preferably 3parts by mass or less, more preferably 2 parts by mass or less, withrespect to 100 parts by mass of the base rubber. In addition, the corerubber composition may further include an organic sulfur compound. Asthe organic sulfur compound, diphenyl disulfides, thiophenols orthionaphthols may be preferably used. The amount of the organic sulfurcompound to be used is preferably 0.1 part by mass or more, morepreferably 0.3 part by mass or more, and is preferably 5.0 parts by massor less, more preferably 3.0 parts by mass or less, with respect to 100parts by mass of the base rubber. The core rubber composition mayfurther include a carboxylic acid and/or a salt thereof. As thecarboxylic acid and/or the salt thereof, a carboxylic acid having 1 to30 carbon atoms and/or a salt thereof is preferred. The amount of thecarboxylic acid and/or the salt thereof to be used is preferably 1 partby mass or more and 40 parts by mass or less, with respect to 100 partsby mass of the base rubber.

The core rubber composition may further include a weight adjusting agentsuch as zinc oxide and barium sulfate, an antioxidant, or a coloredpowder, in addition to the base rubber, the co-crosslinking agent, thecrosslinking initiator, and the organic sulfur compound. The moldingconditions for heat pressing the core rubber composition may bedetermined appropriately depending on the rubber formulation. Generally,the heat pressing is preferably carried out at 130° C. to 200° C. for 10to 60 minutes, or carried out in a two-step heating of heating at 130°C. to 150° C. for 20 to 40 minutes followed by heating at 160° C. to180° C. for 5 to 15 minutes.

[Golf Ball]

In the case that the golf ball according to the present invention is athree-piece golf ball, a four-piece golf ball, and a multi-piece golfball such as a five-piece golf ball and a golf ball comprising more thanfive pieces, examples of the material for an intermediate layer disposedbetween the core and the outmost cover include a thermoplastic resinsuch as a polyurethane resin, an ionomer resin, a polyamide resin, andpolyethylene; a thermoplastic elastomer such as a styrene elastomer, apolyolefin elastomer, a polyurethane elastomer, and a polyesterelastomer; and a cured product of a rubber composition. Herein, examplesof the ionomer resin include a product obtained by neutralizing, with ametal ion, at least a part of carboxyl groups in a copolymer composed ofethylene and an α,β-unsaturated carboxylic acid; and a product obtainedby neutralizing, with a metal ion, at least a part of carboxyl groups ina terpolymer composed of ethylene, an α,β-unsaturated carboxylic acidand an α,β-unsaturated carboxylic acid ester. The intermediate layer mayfurther include a weight adjusting agent such as barium sulfate andtungsten, an antioxidant, and a pigment. The intermediate layer may bereferred to as an inner cover layer or an outer core depending on theconstruction of the golf ball.

The golf ball according to the present invention comprises a golf ballbody and a paint film formed on a surface of the golf ball body, andpreferably has a coefficient of friction (dry) of 0.48 or more and 0.60or less calculated using a contact force tester.

In the present invention, the coefficient of friction calculated usingthe contact force tester is a coefficient of friction between the golfball and a collision plate when the golf ball is allowed to collide withthe collision plate disposed inclined at a predetermined angle to theflying direction of the golf ball. By using the contact force tester, atime function Fn(t) of contact force in a direction perpendicular to thecollision plate and a time function Ft(t) of contact force in adirection parallel to the collision plate are concurrently measured, anda maximum value of a time function M(t) which is a ratio of Ft(t) toFn(t) represented by the following equation is defined as a coefficientof friction.M(t)=Ft(t)/Fn(t)

In the present invention, the method of calculating the coefficient offriction will be described based on FIG. 2 to FIG. 4. FIG. 2 is acontact force tester for measuring the coefficient of friction. FIG. 3is an enlarged cross-sectional view of a collision plate 4 that the golfball is allowed to collide with.

The contact force tester 1 makes pseudo conditions of hitting a golfball with a club face, and enables to measure various forces at thattime. The contact force tester 1 includes, for example, a launcher 5launching a golf ball 2 in an upward and perpendicular direction, and acollision plate 4 positioning on the upper side of the launched golfball 2 and having a striking face 3 that the golf ball 2 collides with.

Since a distance between the launcher 5 and the striking face 3 isrelatively short, an initial velocity of the golf ball 2 corresponds toa collision velocity. This collision velocity corresponds to a headspeed of a club head in an actual golf swing. In view of this point, thecollision velocity of the golf ball 2 to the striking face 3 may be set,for example, within the range of about 10 m/s to about 50 m/s. In thepresent invention, in light of the head speed of approach shots, theinitial velocity is set to 19 m/s.

The desired value of the initial velocity of the golf ball 2 is set bythe volume of a controller 6 or the like. Based on a distance between afirst sensor S1 and a second sensor S2 provided in the launcher 5 and atime difference between interrupting these sensors, the controller 6calculates the actually measured value of the initial velocity of thegolf ball 2, and outputs the value to a computer device PC or the like.

FIG. 3 shows a partially enlarged cross-sectional view of the collisionplate 4. The collision plate 4 can incline the striking face 3 at apredetermined angle α to the launching direction (flying direction) ofthe golf ball 2. In the present invention, an angle θ obtained bysubtracting the angle α from 90 degree is defined as a collision angle.This collision angle θ corresponds to a loft angle of a club face (notshown) in an actual swing. Further, in view of the loft angle of a golfclub, the collision angle θ is set to a plurality of values (e.g. 15°,20°, 35° and the like), for example, within a range from 10° to 90°, andthe measurement of the contact force, which will be described later, canbe conducted at each angle. In the present invention, the collisionangle θ is set to 55° in order to recreate the spin rate on approachshots.

The collision plate 4 comprises, for example, a base plate 4 a formedfrom a metal plate material, a superficial plate 4 c constituting thestriking face 3, and a pressure sensor 4 b interposed therebetween,which are fixed to one another with a bolt 4 d integrally.

The base plate 4 a may be formed from any material without particularlimitation, as long as it has a predetermined strength and rigidity, butpreferably formed from steel. The base plate 4 a preferably has athickness in a range from 5.0 mm to 20.0 mm. A model number of the mainbolt 4 d is, for example, M10 according to JIS.

As the pressure sensor 4 b, for example, a 3-component force sensor ispreferably used. Such sensor can measure, at least, a perpendicularforce Fn in a direction perpendicular to the striking face 3, and ashear force Ft in a direction parallel to the striking face 3 (adirection from the sole side toward the crown side in a club face) astime-series data. The measurement of the force is conducted byconnecting a charge amplifier or the like to the pressure sensor 4 b.

As the pressure sensor 4 b, a variety of products may be used, forexample, a 3-component force sensor (model 9067) manufactured by KistlerInstrument Corporation can be used. This sensor enables to measure forcecomponents in a parallel direction, a Y direction and a perpendiculardirection. Although not illustrated, the measurement of the pressure isconducted by connecting a charge amplifier (model 5011B manufactured byKistler Instrument Corporation) to the pressure sensor 4 b. The pressuresensor 4 b is formed in its center with a through-hole through which themain bolt 4 d is inserted to integrally fix the pressure sensor 4 b tothe base plate 4 a.

The superficial plate 4 c is composed of a main body 4 c 1 and asuperficial material 4 c 2 disposed outside of the main body 4 c 1 toprovide the striking face 3 and having an area large enough to collidewith the golf ball 2. These are fixed with a bolt or the like, which isnot illustrated, in a detachable manner. Accordingly, by appropriatelychanging the material, planner shape and/or surface structure of thesuperficial material 4 c 2, it is possible to create approximate modelsof various kinds of club faces and to measure the contact force thereof.

The main body 4 c 1 may be formed from any material without limitation,but typically formed from stainless steel (SUS-630). The thickness ofthe main body 4 c 1 is typically in a range from 10 mm to 20 mm.Further, the main body 4 c 1 may have a substantially same planner shapeas the pressure sensor 4 b, for example, a square shape with a length of40 mm to 60 mm on one side. Into the main body 4 c 1, the front end ofthe main bolt 4 d is screwed. As a result, the pressure sensor 4 b isinterposed between the base plate 4 a and the main body 4 c 1, and theposition thereof is fixed.

The superficial material 4 c 2 providing the striking face 3 of thecollision plate 4 may adopt various materials, planner shapes andsurface structures, however, it is preferably formed from the samematerial as the face (not shown) of the golf club head which has beenset as an analysis subject beforehand. In the present invention, in viewof evaluating a model of approach shots, SUS-431 stainless steel whichis the same material as the head material of CG-15 manufactured byCleveland Golf is used as the superficial material 4 c 2. The thicknessof the superficial material 4 c 2 may be arbitrarily changed, forexample, within a range of 1.0 mm to 5.0 mm. The planner shape of thesuperficial material 4 c 2 may be substantially the same as that of themain body 4 c 1, for example, a square shape with a length of 40 mm to60 mm on one side.

The contact force tester 1 comprises a strobe device 7 and a high speedtype camera device 8 enabling to take a photograph of the collisionbetween the golf ball 2 and the striking face 3 as well as the golf ball2 rebounding from the striking face 3. The strobe device 7 is connectedto a strobe power 9. The camera device 8 is connected to a camera power10 via a capacitor box. The imaged data is memorized in the computerdevice PC or the like. By comprising these devices, a slipping velocityand a contact area at the time of the collision between the golf ball 2and the striking face 3, and a launch speed, a launch angle and abackspin rate of a golf ball, which will be explained later, can bemeasured.

FIG. 4 shows a time history of the perpendicular force Fn and the shearforce Ft applied to the striking face 3 at the time of the collision bythe golf ball 2 measured with the contact force tester 1 under aspecific condition.

FIG. 4 is a graph illustrating an example of Fn(t) and Ft(t) measuredwith the tester shown in FIGS. 2 and 3. In FIG. 4, a point P0 representsa point where the pressure sensor 4 b starts sensing force, andgenerally corresponds to the point at which the striking face 3 and thegolf ball 2 come into collision with each other. Fn(t) which is acontact force in the perpendicular direction gradually increases fromthe point P0, peaks at a point P4, and comes down therefrom to reachzero at a point P3. The point P3 represents a point where the pressuresensor 4 b no longer senses force, and generally corresponds to thepoint where the golf ball 2 leaves the striking face 3.

On the other hand, the value of Ft(t) which is a contact force (i.e.,shear force) in the direction parallel to the collision plate increaseswith time from the point P0, peaks at a point P1, and comes downtherefrom to reach zero at a point P2 after which it takes a negativevalue. Since the golf ball leaves the pressure sensor 4 b at the pointP3, the curve of Ft(t) sensed by the pressure sensor 4 b takes zero atthe point P3. An area S1 of the region where Ft(t) takes a positivevalue within the region surrounded by the curve of Ft(t) and the timeaxis represents impulse where the shear force is positive. On the otherhand, an area S2 of the region where Ft(t) takes a negative value withinthe region surrounded by the curve of Ft(t) and the time axis representsimpulse where the shear force is negative. Impulse S1 acts in adirection promoting back spin, and impulse S2 acts in a directioninhibiting back spin. Here, impulse S1 takes a larger value than impulseS2, and a value obtained by subtracting impulse S2 from impulse S1contributes to back spin of a golf ball.

A coefficient of friction can be obtained by calculating a maximum valueof M(t) which is expressed by Ft(t)/Fn(t).

In the present invention, the coefficient of friction (dry) obtained asdescribed above is preferably 0.48 or more, more preferably 0.49 ormore, even more preferably 0.50 or more, and is preferably 0.60 or less,more preferably 0.58 or less, even more preferably 0.56 or less. If thecoefficient of friction falls within the above range, the spin rate onapproach shots becomes better.

Further, in the present invention, when measuring the coefficient offriction as described above, a wet paper having slits formed thereon isattached on the surface of the collision plate, and the measuredcoefficient of friction (wet paper slit) is preferably 0.18 or more,more preferably 0.19 or more. The coefficient of friction (wet paperslit) measured by attaching the wet paper can be used to evaluatecontrollability on approach shots from the rough. If the coefficient offriction (wet paper slit) falls within the above range, the golf ballaccording to the present invention is also excellent in controllabilityon approach shots from the rough.

EXAMPLES

Hereinafter, the present invention will be described in detail by way ofexamples. However, the present invention is not limited to the examplesdescribed below, and various changes and modifications without departingfrom the gist of the present invention are included in the scope of thepresent invention.

[Evaluation Method]

(1) Measurement of Coefficient of Friction (Dry)

The contact force tester shown in FIG. 2 was used to measure thecoefficient of friction (dry) of the golf ball.

-   1. Specification of tester    -   (A) Launcher: air gun system    -   (B) Collision plate:        -   Base plate 4 a            -   Steel            -   Thickness: 5.35 mm        -   Superficial plate 4 c            -   Main body 4 c 1                -   Size: 56 mm×56 mm×15 mm                -   Stainless steel (SUS-630)            -   Superficial material 4 c 2                -   Size: 56 mm×56 mm×2.5 mm                -   Metal composition: SUS-431                -   Groove shape: see FIG. 5        -   Angle of inclination (α)            -   35 degrees (to flying direction of golf ball)    -   (C) Pressure sensor 4 b        -   3-component force sensor (model 9067) available from Kistler            Instrument Corporation    -   Charge amplifier        -   Model 5011B available from Kistler Instrument Corporation    -   (D) Capture of contact force into PC

A pulse counter board PCI-6101 (manufactured by Interface Corporation)was used. With a 16-bit PCI pulse counter board having 4 channels,measurement suited for a specific application may be realized in fourcounter modes. The maximum input frequency is 1 MHz.

As shown in FIG. 5, the groove structure of a sand wedge CG-15 availablefrom Cleveland Golf is reproduced on the striking face 3 of thecollision plate 4. As shown in FIG. 5 (a), on the striking face 3, largegrooves (zip grooves) are formed, and a plurality of small grooves areformed on the surface between the large grooves (zip grooves). FIG. 5(b) is an enlarged view of cross-section structure of the zip groove.The dimensions of the zip groove are as follow.

Zip groove (groove) width W: 0.70 mm

Zip groove (groove) depth h: 0.50 mm

Zip groove (groove) pitch: 3.56 mm

Zip groove (groove) angle α: 10°

Zip groove shoulder R: 0.25

A plurality of small grooves between the zip grooves are formed by alaser-milling method such that the surface portion between the zipgrooves has a surface roughness Ra=2.40±0.8 μm and Rmax=14.0±8 μm. It isnoted that the surface roughness Ra and Rmax are measured by usingSJ-301 manufactured by Mitsutoyo Corporation under the conditions ofspecimen length=2.5 mm and cut off value=2.5 mm.

(2) Measuring Procedure

The coefficient of friction was measured according to the followingmethod.

-   -   (a) Setting the angle (α) of the collision plate at 35 degrees        to the flying direction (vertical direction) of the golf ball;    -   (b) Adjusting the air pressure of the launcher 5;    -   (c) Launching the golf ball from the launcher (launch speed: 19        m/s);    -   (d) Measuring the initial velocity of the golf ball from the        preset distance between the sensor S1 and sensor S2 and the time        difference between the times for the golf ball to interrupt the        sensors S1 and S2;    -   (e) Measuring the contact force Fn(t) and contact force Ft(t),        and calculating the maximum value of Ft(t)/Fn(t).        (3) Result of Measurement

One example of the results obtained with the above tester in the abovemeasuring procedure is shown in FIG. 6. From FIG. 6, the value of M(t)was calculated as Ft(t)/Fn(t), and the maximum value thereof was 0.58.Since noise tends to generate in initial period where the contact forcerises up and in terminal period for measuring Ft and Fn, the maximumvalue of M(t) was calculated after trimming an early stage of theinitial period and late stage of the terminal period.

(2) Measurement of Coefficient of Friction (Wet Paper Slit)

As shown in FIG. 7, slits were formed at an interval of 5 mm on Sontarmaintenance cloth thick type (size: 56 mm×56 mm) manufactured by E. I.du Pont de Nemours and Company, and the cloth was wetted with water andattached on the collision plate. At this time, the cloth was attachedsuch that the grooves formed on the collision plate and the slits areperpendicular to one another. Except that the launch speed of the golfball was changed to 9 m/s, the coefficient of friction (wet paper slit)and spin rate were measured by the same method and under the sameconditions as those in the measurement of the coefficient of friction(dry). It is noted that the spin rate is represented by a spin ratedifference obtained by subtracting the spin rate of Golf ball No. 9 fromthat of each golf ball.

(3) Mechanical Properties of Paint Film

A paint obtained by blending the base material and curing agent wasdried and cured at 40° C. for 4 hours to prepare a paint film. Accordingto JIS-K7161, this paint film was punched as a dumbbell shape to preparea test piece, and the physical properties of the test piece weremeasured by using a tensile tester manufactured by Shimadzu Corporation,and the elastic modulus of the test piece at 10% elongation wascalculated.

Thickness of test piece: 0.05 mm

Tension speed: 50 mm/min

(4) Spin Rate and Launch Angle on Approach Shots for Less than 40 Yards

A sand wedge (CG 15 forged wedge (52°) available from Cleveland Golf)was installed on a swing robot M/C manufactured by True Temper Sports,Inc. The golf ball was hit at a head speed of 21 m/sec, and the spinrate (rpm) thereof was measured by continuously taking a sequence ofphotographs of the hit golf ball. This measurement was conducted tentimes for each golf ball, and the average value thereof was adopted asthe spin rate. The launch angle was determined by measuring, with aunidimensional CCD sensor, the shadow of the ball passing through alight screen that was emitted from a linear laser light source locatedin front of the direction of hitting the ball with the swing robot M/C.The launch angle and spin rate are represented by a difference obtainedby subtracting the launch angle and spin rate of Golf ball No. 9 fromthose of each golf ball.

(5) Shot Feeling

An actual hitting test was carried out by ten amateur golfers (highskilled persons) using a sand wedge (CG 15 forged wedge (52°) availablefrom Cleveland Golf). In accordance with the number of people whoanswered the shot feeling was good (feeling like that the golf ball waslifted on the club face, feeling like that the golf ball gripped on theclub surface, feeling like that the spin was imparted, feeling like thatthe golf ball was stuck on the club face, etc.), the golf balls wereevaluated as follows.

E (Excellent): 9 or more

G (Good): 6 to 8

F (Fair): 3 to 5

P (Poor): 2 or less

(6) Compression Deformation Amount (mm)

The deformation amount of the core or golf ball along the compressiondirection (shrinking amount of the core or golf ball along thecompression direction), when applying a load from 98 N as an initialload to 1275 N as a final load to the core or golf ball, was measured.

[Production of Three-Piece Golf Ball]

(1) Production of Spherical Core

The core rubber composition having the formulation shown in Table 1 wasmixed and kneaded, and heat-pressed in upper and lower molds, eachhaving a hemispherical cavity, at 170° C. for 20 minutes to obtain thespherical core having a diameter 39.7 mm.

TABLE 1 Core composition Parts by mass Polybutadiene rubber 100 Zincacrylate 38 Zinc oxide 5 Barium sulfate Appropriate amount*) Diphenyldisulfide 0.5 Dicumyl peroxide 0.8 Diameter (mm) 39.7 Surface hardness(Shore D) 58 Center hardness (Shore D) 41 Compression deformation amount(mm) 2.7 *)Adjustment was made such that the golf ball had a mass of45.3 g. Polybutadiene rubber: “BR730 (high cis-polybutadiene)”manufactured by JSR Corporation Zinc acrylate: ZN-DA90S (product of 10%zinc stearate coating) manufactured by Nihon Jyoryu Kogyo Co., Ltd. Zincoxide: “Ginrei R” manufactured by Toho Zinc Co., Ltd. Barium sulfate:“Barium Sulfate BD” manufactured by Sakai Chemical Industry Co., Ltd.Diphenyl disulfide: manufactured by Sumitomo Seika Chemicals Co., Ltd.Dicumyl peroxide: “Percumyl (register trademark) D” manufactured by NOFCorporation(2) Preparation of Intermediate Layer Composition and Cover Composition

The materials having the formulations shown in Tables 2, 3 were mixedwith a twin-screw kneading extruder to prepare the intermediate layercomposition and cover composition in a pellet form. The extrudingconditions were a screw diameter of 45 mm, a screw rotational speed of200 rpm, and screw L/D=35, and the mixtures were heated to 200° C. to260° C. at the die position of the extruder.

TABLE 2 Intermediate layer composition Parts by mass Himilan 7337 50Himilan AM7329 50 Slab hardness (Shore D) 65 Himilan 7337: zinc ionneutralized ethylene-methacrylic acid copolymer ionomer resinmanufactured by Du Pont-Mitsui Polychemicals Co., Ltd. Himilan AM7329:sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resinmanufactured by Du Pont-Mitsui Polychemicals Co., Ltd.

TABLE 3 Cover composition Parts by mass Elastollan XNY85A 100 Titaniumoxide 4 Slab hardness (Shore D) 32 Elastollan XNY85A: thermoplasticpolyurethane elastomer (Shore D hardness: 32) manufactured by BASF JapanLtd(3) Production of Intermediate Layer

The intermediate layer composition obtained above was directly injectionmolded on the spherical core obtained as described above to produce theintermediate layer. Upper and lower molds for molding have ahemispherical cavity and a retractable hold pin holding the sphericalcore. When molding the intermediate layer, the hold pin was protruded tohold the spherical core after the spherical core was charged, and theintermediate layer composition heated to 260° C. was charged for 0.3second into the mold held under a pressure of 80 tons, and cooled for 30seconds to mold the intermediate layer (thickness: 1 mm).

(4) Molding of Half Shell

The compression molding of the half shells was conducted by charging apellet of the cover composition into each of the depressed part of thelower mold for molding half shells, and applying pressure to mold halfshells. The compression molding was conducted under the conditions of amolding temperature of 170° C., a molding time of 5 minutes and amolding pressure of 2.94 MPa.

(5) Molding of Cover

The spherical body having the intermediate layer covered thereon andobtained in (3) was concentrically covered with two of the half shellsobtained in (4), and the spherical body and two of the half shells werecompression molded to obtain the cover (thickness: 0.5 mm). Thecompression molding was conducted under the conditions of a moldingtemperature of 145° C., a molding time of 2 minutes and a moldingpressure of 9.8 MPa.

(6) Preparation of Paint

The materials shown in Table 4 were blended to prepare the paintcompositions. The surface of the golf ball body obtained above wassubjected to a sandblast treatment, and a mark was formed thereon. Then,the paint was applied to the golf ball body with a spray gun, and thepaint was dried in an oven of 40° C. for 24 hours to obtain the golfball having a diameter of 42.7 mm and a mass of 45.3 g. The thickness ofthe paint film was set in a range of from 20 μm to 40 μm. The golf ballbody was placed in a rotating member shown in FIG. 8, the rotatingmember was allowed to rotate at 300 rpm, and application of the paintwas conducted by spacing a spray distance (7 cm) between the air gun andthe golf ball body while moving the air gun in an up and down direction.The painting interval in the overpainting operation was set to 1.0second. Application of the paint was conducted under the air gunspraying conditions of a spraying air pressure: 0.15 MPa, a compressedair tank pressure: 0.10 MPa, a painting time for one application: 1second, an atmosphere temperature: 20° C. to 27° C., and an atmospherehumidity: 65% or less. Results evaluating the spin performance of theobtained golf balls are shown in Table 4.

TABLE 4 Golf ball No. 1 2 3 4 5 Base material Polyrotaxane — 36 50 70100 formulation Polycaprolactone polyol 56 36 28 17 — (parts by mass)Modified product of vinyl 44 28 22 13 — chloride-vinyl acetate copolymerModified silicone 0.1 0.10 0.1 0.1 0.1 Dibutyl tin dilaurate 0.01 0.010.01 0.01 0.01 Solvent 100 100 100 100 100 Polyn #950 — — — — — Curingagent HDI biuret-modified product — — — — — formulation HDI isocyanurate100 100 100 100 100 (parts by mass) IPDI isocyanurate — — — — — Solvent100 100 100 100 100 Mixing ratio of curing agent/base material 1.2/1.01.2/1.0 1.2/1.0 1.2/1.0 1.2/1.0 (NCO/OH molar ratio) 10% elastic modulusof paint film (kgf/cm²) 35 8 8 8 8 Physical Compression deformation 2.652.65 2.65 2.65 2.65 properties of amount (mm) golf ball Spin rate ofgolf ball (rpm) 370 480 520 550 590 Launch angel (°) −1.72 −1.98 −2.06−2.21 −2.39 Coefficient of friction (dry) 0.42 0.49 0.51 0.54 0.57Coefficient of friction 0.13 0.20 0.24 0.24 0.23 (wet paper slit) Spinrate difference 90 570 680 675 620 (wet paper slit) Shot feeling E E E EE Golf ball No. 6 7 8 9 10 Base material Polyrotaxane — — — — —formulation Polycaprolactone polyol — — — — — (parts by mass) Modifiedproduct of vinyl — — — — — chloride-vinyl acetate copolymer Modifiedsilicone — — — — — Dibutyl tin dilaurate — — — — — Solvent — — — — —Polyn #950 100 100 100 100 100 Curing agent HDI biuret-modified product30 30 30 30 30 formulation HDI isocyanurate 30 30 30 30 30 (parts bymass) IPDI isocyanurate 40 40 40 40 40 Solvent 100 100 100 100 100Mixing ratio of curing agent/base material 0.38/1.0 0.5/1.0 0.8/1.01.2/1.0 1.6/1.0 (NCO/OH molar ratio) 10% elastic modulus of paint film(kgf/cm²) 8 38 126 186 275 Physical Compression deformation 2.65 2.652.65 2.65 2.65 properties of amount (mm) golf ball Spin rate of golfball (rpm) 390 360 255 0 −75 Launch angel (°) −1.64 −1.44 −1.01 0 0.29Coefficient of friction (dry) 0.46 0.42 0.38 0.32 0.28 Coefficient offriction (wetted 0.17 0.16 0.15 0.13 0.11 paper slit) Spin ratedifference (wetted 300 220 160 0 −80 paper slit) Shot feeling E G G F P

The raw materials used in Table 4 are shown below.

Base Material

Polyrotaxane: “SeRM (registered trademark) super polymer SH3400P (apolyrotaxane having a cyclodextrin, at least a part of hydroxyl groupsthereof being modified with a caprolactone chain via —O—C₃H₆—O— group, alinear molecule of polyethylene glycol and a blocking group of anadamantyl group; molecular weight of linear molecule: 35,000, hydroxylvalue: 72 mg KOH/g, total molecular weight of polyrotaxane: 700,000 inweight average molecular weight) manufactured by Advanced SoftmaterialsInc.

Polycaprolactone polyol: Placcel 308 manufactured by Daicel ChemicalIndustries, Ltd.

Modified product of vinyl chloride-vinyl acetate copolymer: Solbin AL(hydroxyl-modified vinyl chloride-vinyl acetate copolymer) manufacturedby Nissin Chemical Industry Co., Ltd.

Modified silicone: DBL-C31 manufactured by Gelest, Inc.

Solvent: mixed solvent of xylene/methylethyl ketone=70/30 (mass ratio)

Polin #950: urethane polyol having a hydroxyl value of 128 mg KOH/g andformed from a polyol component (trimethylolpropane andpolyoxytetramethylene glycol) and a polyisocyanate component (isophoronediisocyanate), manufactured by Shinto Paint Co., Ltd.

Curing Agent

Isocyanurate of hexamethylene diisocyanate (HDI isocyanurate): DuranateTKA-100 (NCO content: 21.7%) manufactured by Asahi Kasei ChemicalsCorporation

Biuret-modified product of hexamethylene diisocyanate (HDIbiuret-modified product): Duranate 21S-75E (NCO content: 15.5%)manufactured by Asahi Kasei Chemicals Corporation

Isocyanurate of isophorone diisocyanate (IPDI isocyanurate): VESTANATT1890 (NCO content: 12.0%) manufactured by Degussa Co., Ltd.

Solvent: methylethyl ketone

It is apparent from the results of Table 4 that the following golf ballshows low launch angle and high spin rate on approach shots for lessthan 40 yards, in particular, on approach shots around the green (about10 yards to 20 yards), and thus exhibits excellent controllability. Saidgolf ball comprises a golf ball body and a paint film formed on asurface of the golf ball body, wherein the paint film is formed from apaint composition including a polyisocyanate and a polyrotaxane, andwherein the polyrotaxane has a cyclodextrin, a linear molecule piercingthrough the cyclic structure of the cyclodextrin, and having blockinggroups located at both ends of the linear molecule to preventdisassociation of the cyclodextrin.

The present invention is useful for painted golf balls. This applicationis based on Japanese patent application No. 2014-232205 filed on Nov.14, 2014, the content of which is hereby incorporated by reference.

The invention claimed is:
 1. A golf ball comprising a golf ball body anda paint film formed on a surface of the golf ball body, wherein thepaint film is formed from a curing type paint composition including: abase material containing a polyrotaxane and at least one polyol selectedfrom the group consisting of a polyether polyol, a polyester polyol, apolycaprolactone polyol, a polycarbonate polyol, and an acrylic polyol,and a curing agent containing a polyisocyanate; and wherein thepolyrotaxane comprises a cyclodextrin, and a linear molecule included inthe cyclodextrin cyclic structure in a manner of piercing through thecyclic structure of the cyclodextrin, the linear molecule havingblocking groups located at both ends of the linear molecule to preventdisassociation of the cyclodextrin, and at least a portion of thecyclodextrin hydroxyl groups being modified with a caprolactone chainexpressed by —(CO(CH₂)₅O)nH via a —O—C₃H₆—O— group, wherein n representsthe degree of polymerization and is a natural number of 3 to 40, and aresin component of the base material contains the polyol in an amount of5 mass % or more and 90 mass % or less.
 2. The golf ball according toclaim 1, wherein the base material contains at least one polyol selectedfrom the group consisting of the polyester polyol, the polycaprolactonepolyol, the polycarbonate polyol, and the acrylic polyol.
 3. The golfball according to claim 1, wherein the linear molecule is polyethyleneglycol, and the blocking group is an adamantyl group.
 4. The golf ballaccording to claim 1, wherein the resin component of the base materialcontains the polyrotaxane in an amount of 10 mass % or more and 90 mass% or less.
 5. The golf ball according to claim 1, wherein the resincomponent of the base material contains the polyol in an amount of 10mass % or more and 80 mass % or less.
 6. The golf ball according toclaim 1, wherein the curing type paint composition further includes avinyl chloride-vinyl acetate copolymer and/or a modified productthereof.
 7. The golf ball according to claim 1, wherein the curing typepaint composition further includes a modified silicone.
 8. The golf ballaccording to claim 7, wherein the modified silicone is included in anamount of 0.01 part by mass or more and 10 parts by mass or less withrespect to 100 parts by mass of the resin component of the basematerial.
 9. The golf ball according to claim 1, wherein thepolyisocyanate includes an isocyanurate-modified product ofhexamethylene diisocyanate.
 10. The golf ball according to claim 1,wherein the linear molecule has a weight average molecular weightranging from 5,000 to 100,000.
 11. The golf ball according to claim 1,wherein a ratio of the hydroxyl groups modified with the caprolactonechain to all the hydroxyl groups included in the cyclodextrin before themodification is 2 mole % or more.
 12. The golf ball according to claim1, wherein the polyrotaxane has a hydroxyl value ranging from 10 mgKOH/g to 400 mg KOH/g.
 13. The golf ball according to claim 1, whereinthe polyrotaxane has a weight average molecular weight ranging from30,000 to 3,000,000.
 14. The golf ball according to claim 6, wherein thevinyl chloride-vinyl acetate copolymer and/or the modified productthereof includes a hydroxyl group-modified vinyl chloride-vinyl acetatecopolymer.
 15. The golf ball according to claim 6, wherein the vinylchloride-vinyl acetate copolymer and/or the modified product thereof isincluded in an amount of 4 mass % or more and 50 mass % or less in theresin component of the base material.
 16. The golf ball according toclaim 1, wherein the paint film has a 10% elastic modulus of 160 kgf/cm²or less.
 17. The golf ball according to claim 1, wherein the golf ballbody comprises a core and a cover covering the core, and the cover has aslab hardness of 70 or less in Shore D hardness.
 18. The golf ballaccording to claim 1, wherein the golf ball has a coefficient offriction (dry) ranging from 0.48 to 0.60, and a coefficient of friction(wet paper slit) of 0.18 or more.
 19. A golf ball comprising a golf ballbody and a paint film formed on a surface of the golf ball body, whereinthe paint film is formed from a curing type paint composition including:a base material containing a polyrotaxane and a polycaprolactone polyolhaving a weight average molecular weight in a range from 600 to 8000,and a curing agent containing a polyisocyanate; and wherein thepolyrotaxane comprises a cyclodextrin, and a linear molecule included inthe cyclodextrin cyclic structure in a manner of piercing through thecyclic structure of the cyclodextrin, the linear molecule havingblocking groups located at both ends of the linear molecule to preventdisassociation of the cyclodextrin, and at least a portion of thecyclodextrin hydroxyl groups being modified with a caprolactone chainvia —O—C₃H₆—O— group, and a resin component of the base materialcontains the polyol in an amount of 5 mass % or more and 90 mass % orless.